In commerce, it is often necessary to move or transport large quantities of goods into and out of transportation vehicles such as trucks. For example, in the dairy industry, large semi-trailer trucks may be backed up to the loading dock of a dairy and may be loaded with generally box-like, rectangular, basket-type containers bearing cartons of milk, butter, cheese and the like for transportation to retail stores. The containers are stacked one upon another to a heighth of, for example, five feet and are also stacked side-by-side in columns and rows. At present, it is common for one to employ a small hand truck to lift up one stack of containers at a time and transport it into or out of the truck. This procedure takes a long time, and care must be taken to precisely locate the stacks of containers in the truck so that as the truck stops at various stores, each store receives the merchandise that it had ordered. At the same time as the ordered, containerized goods are delivered, empty containers are commonly picked up by the truck.
Various devices have been devised to automatically load trucks with containerized goods. One such device is shown in U.S. Pat. No. 3,186,566, in which interlocking containers are stacked upon a sled which is then pushed by a wheeled, cable-drawn carriage into a truck. Other loading devices are shown in U.S. Pat. Nos. 2,820,560, 3,741,413, 3,704,798, 2,422,798, 2,422,910, 3,788,500, 766,866, 2,421,128 and 2,513,752. It is also known that stacks of containers, such as are used in dairies, may be pulled across the floor by a cable-drawn bar, the crates resting on a floor such as a concrete floor and the cables being attached at one end to a winch drum and at the other end to an end of the bar.
As shown in U.S. Pat. No. 3,186,566, cables or drive chains generally ride in one or more grooves formed in the floor surface, and as a result, their installation requires the expensive and time-consuming job of removing and repairing a long section of flooring to provide the slots or grooves. Further, in the event that cables attached to the ends of a bar are employed, it has been found difficult to maintain uniform tension between the two cables so that the load moves in a straight line. If one cable is slightly shorter than the other, then the load may be skewed slightly toward one side or the other of its intended path of travel, making it difficult to transport the load centrally through a dock doorway.